1. Field of the Invention
The invention relates to a configuration for an ink jet print head, which is composed of a plurality of stacked modules, or is equipped with only one module.
Such ink jet print heads are used both in office printers and in small high-speed printers--of the kind needed for postage meters and product labeling devices--and as a rule have a relatively large number of jets.
Precisely in this latter application, high reliability is required, so that errors in printing, which can entail major subsequent costs, are avoided.
A component that has an especially strong influence on the reliability of the printer is the ink jet print head. If the ink jet print head is composed of a plurality of components, the precise arrangement thereof to one another and with one another has a definitive influence on its reliable function. The reliability is also known to increase as the number of individual parts decreases. It is at these two points that the invention comes in.
2. Description of the Related Art
The prior art has known a system wherein, in an ink jet print head composed of a plurality of ink jet printing modules, at least one ribbon conductor is connected to each module by way print control and feeding of electric current are effected from a central point. See, for instance, German patent publications DE 44 43 244 A1 and DE 44 43 245 A1 and U.S. Pat. No. 4,703,333.
Each module of U.S. Pat. No. 4,703,333 has a number of jets and is formed of a plurality of stacked plates with ink jet printing chambers and ink supply conduits machined into them. The module is embodied by the sideshooter principle; that is, the nozzle conduits or nozzle openings extend crosswise through an outer plate. The pressure wave in the ink jet printing chamber is in the direction of the jet channel, so that the ink droplets are expelled orthogonally to the plate. Correspondingly, ink inlet channels and openings for the ink supply are provided crosswise through the outer plate on the opposite side of the module. To that end, an inlet stub is mounted on the plate above each ink inlet openings. The inlet stubs, all in a row, of all the modules are connected to an ink tank via a common adapter and an ensuing ink hose. The adapter is constructed as an ink distributor element. Stubs that are slipped onto the inlet stubs of the modules are located on its ink outlet side. On its ink inlet side, there is one stub, onto which the ink hose is slipped. The problem of equalizing pressure for the ink inlet is not taken into account here. For reasons of both unhindered ink expulsion--via a side wall, because this is a sideshooter--and also the space required for the ink inlet, a staggered arrangement of the modules is necessary for this ink jet print head. In other words, the modules are stacked, inclined, one after another in such a way that the jet region on one side and the ink supply region on the other are free. This in turn dictates a correspondingly large amount of space required.
A receiving frame for the modules is provided which is adapted to the staggered arrangement. The frame has oblique steps--one step per module--and one common opening for the jet region of all the modules. To achieve the lateral offset of the jets relative to one another, the modules are provided with oblong slots through which screws are passed that engage threaded holes in the steps. The modules must be adjusted with a gauge and then locked by means of the screws.
As can be seen from this description, the number of individual parts and the adjustment effort and expense are considerable. A cleaning and sealing station adapted to this ink jet print head will be very complicated in its construction, because of the stepped configuration.
An ink jet print head of stacked construction made of individual identical modules is also known. The modules operate by the edgeshooter principle and are joined together by the "interlaced principle". See European patent disclosure EP 0 615 844 B1.
The modules are secured in a module carrier, held at the spacing from one another by means of spacers. The module carrier has a front panel with one common opening for the nozzle faces of all the modules and with separate fastening elements for each module. Stop edges for the module, offset from one another, are machined into the opening. Each module accordingly has one reference edge with a highly accurate spacing from the first jet of its row of jets. That configuration results in the offset arrangement by the interlaced principle.
The individual module comprises three plates stacked one above the other: a middle plate and two cover plates. The jets are formed into one of the cover plates in such a way that the middle plate forms a jet wall or nozzle wall.
The spacers are attached to the modules in such a way that the rows of jets of the modules are kept equidistant from one another. Three spacers per module are provided, so that the spacing is defined by three-point contact. The spacing is determined by the length of the spacers, since these spacers are in a row, touching one another. The modules are accordingly provided with three continuous bores, through which the spacers are passed. The spacers are also designed such that in the peripheral region they rest on the face of the middle plate of the module that is involved in forming the jets.
In their contact region with the middle plate, the spacers are secured by means of adhesive bonding or soldering.
In this embodiment, the tolerances of the spacers and of the fastening means determine the accuracy of the spacing of the rows of jets from one another. Depending on the number of modules, the tolerances in the chain of tolerances add up.
Finally, it is also known to assemble an ink jet print head from three modules by the "noninterlaced" principle. See Third Annual European Ink Jet Printing Workshop, Maastricht, Holland, Oct. 16-18, 1995. Slits of equal length, which are parallel and aligned with one another and extend obliquely, are made in a front panel, and modules are inserted by their jet region into these slits. The recording carrier is moved past the rows of jets in such a way that the printed image is composed of three stripes one above the other. For a vertical solid line, accordingly the upper third is generated by the first module, the middle third by the second module, and the lower third by the third module.